In various electronic circuits such as diversity signal reception of microwave downconverters, it is desirable to know the signal levels into each diversity receiver, and to be able to use a signal level monitoring voltage to control a data switch to choose the stronger level signal. While such signal monitoring devices are available in the prior art, they are not only very expensive, but a typical measuring range of such a commercial device is only in the neighborhood of 50 dB. The expense of such a device is typically in the neighborhood of thousands of dollars. The present invention, on the other hand, is able to measure a signal range greater than 60 dB in one embodiment of the invention with an estimated manufacturing cost of much less than $100. Thus, the present invention numerically has several orders of magnitude greater signal measuring range while also having more than an order of magnitude lower cost.
The present invention does not directly detect (and thus does not interfere with) the actual signal applied to the receiver, but rather detects the amplitude of the IF output and feedback signals around the delayed automatic gain control circuit (AGC), and combines these two signals in such a manner that a composite linearly changing dc signal is obtained directly proportional to the decibel level of the signal applied to the gain control circuit. For the purposes of definition in this specification, a Delayed AGC circuit is one where the application of AGC does not start until the input (or output) signal level rises to a certain (predetermined) level.
It is, therefore, an object of the present invention to provide an improved received signal level monitor.